Generally, a light emitting diode (LED) is a kind of semiconductor device, and it converts an electrical signal into infrared ray or light by using a characteristic of a compound semiconductor, to send or receive a signal. The LED is used for home appliances, a remote controller, an electronic display board, a display device, a variety of automation apparatuses and the like.
An operation principle of the LED will be briefly described in the following.
When a forward voltage is applied to a semiconductor of a specific chemical element, electrons and holes are recombined with each other while moving through a positive-negative junction. The recombination of the electrons and the holes causes an energy level to fall down, so that light is emitted.
The LED is generally manufactured to have a very small size of 0.25 mm2 and is mounted on a printed circuit board (PCB) or a lead frame using an epoxy mold.
Representative of the LEDs is a plastic package of 5 mm (T 1¾) or a new package being developed in a specific application field.
A color of light emitted from the LED is determined by a wavelength obtained depending on a combination of elements constituting a semiconductor chip.
Particularly, as an information communication apparatus is in a trend of a small-size and slimness, the communication apparatus has more miniaturized parts such as a resistance, a condenser, and a noise filter. The LED is manufactured in a form of a surface mounted device (hereinafter, referred to as “SMD”) so as to be directly mounted on a printed circuit board (hereinafter, referred to as “PCB”).
Accordingly. an LED lamp for a display device is being developed in the form of the SMD. Such an SMD can substitute a related-art simple lamp. The SMD is used for a lamp display, a character display, an image display and the like that express various colors.
Further, as a high-density integration technology for a semiconductor device is developed and a consumer prefers a more compact electronic product, Semiconductor Mounting Technology (SMT) is widely used, and a packaging technology of the semiconductor device employs a technology for minimizing an installation space such as a Ball Grid Array (BOA), a wire bonding, and a flip chip bonding.
FIG. 1 is a view illustrating a process for fabricating a light emitting diode according to the related art.
As shown in FIG. 1, a gallium nitride (GaN) buffer layer 101 is formed on a sapphire substrate 100 formed of Al2O3. After that, a GaN layer 103, which is not doped with dopants (Hereinafter, referred to as “undoped”), is formed on the GaN buffer layer 101.
In order to form a Group 3-based element in a form of a thin film on the sapphire substrate 100 as described above, a metal organic chemical vapor deposition (MOCVD) is generally used. At this time, the thin film layer is formed under a constant growth pressure.
An N-type GaN layer 105 is formed on the =doped GaN layer 103, and silicon using silane (SiH4) or disilane (Si2H6) gases is used to form the N-type GaN layer 105.
After the N-type GaN layer 105 is formed, an active layer 109 is formed on the N-type GaN layer 105. The active layer 109 functioning as a light emission region is a semiconductor layer having an illuminant formed of a indium gallium nitride(InGaN).
After the active layer 109 is formed, a P-type GaN layer 110 is subsequently formed.
The P-type GaN layer 110 is in a contrast to the N-type GaN layer 105. Namely, electrons are drifted by an external voltage in the N-type GaN layer 105, while holes are drifted by the external voltage in the P-type GaN layer 110. Therefore, the holes and the electrons are mutually recombined in the active layer 109, thereby emitting light.
A transparent metal(TM) layer using a transparent Indium-Tin-Oxide (ITO) metal is formed on the P-type GaN layer 110 so that light generated at the active layer 109 is transmitted and emitted to the external.
After the TM layer is formed, a P-type electrode is formed to complete the LED.
However, the LED constructed as above has a drawback in that a strain is increased due to an inconsistency of the lattice constants between the InGaN layer of the active layer and the GaN layer, thereby reducing an amount of light generated in the active layer.
Further, the inconsistency of the lattice constant deteriorates a product reliability of the LED.
Also, there is a drawback in that the active layer, which is formed on the N-type GaN layer adjacent to the active layer in a form of a two-dimensional plane, has a lower luminous intensity than a three-dimensional formation.